Combination radio and television receiving system



Sept. 23, 1952 w. R. KOCH 2,611,818

COMBINATION RADIO AND TELEVISION RECEIVING SYSTEM Filed Deo. I, 1949 ./i fi/D f @.1 Zj/ZT'M wsrf/MMM@ l a 155 Z0 .fi

HNVENTOR entre!) sTATEs rarest ori-flics COMBINATGN RADIO AND TELEVISION a l RECEIVING SYSTEM Winfield R. Koch, Mai-lion, N.f.r.`,"`assignor to Radio Corporation oi of Delaware America, Va y corporation Application December 1, 1949,v Serial Nopll" The present invention relates to improvements in radio receiving systems and more particularly, although not necessarily exclusively, to combination type radio receiving equipments adapted to receive a plurality of different type signal cornmunications transmitted on respectively different radio carriers of different carrier frequencies bearing different modes of modulation.

In more particularity, the present invention deals with an improved-form of combination type receiving system nding ready application to receiving circuits such kto enable reception of standard broadcast kAM signals through the agency of standard television receiving circuits.

Present-day trends in the design of home instruments for the reception and reproduction of the various commercial radio broadcasting signals such as television FM broadcast, AM broadcast, etc. seem to emphasize the desirability of combining circuit functions so as to more economically provide, in a single instrument, facilities for receiving a plurality of the variousr radio entertainment channels.

In the case -of present-day television receivers which incorporate separate receiving channels for television AM and FM television sound intelligence, there is afforded a good opportunity for re-circuiting some of the electron elements to aid in the reception of other forms of communication. For instance, by extending the range of the radio` frequency tuner section of the television receivenit is quite possible to economically provide a very satisfactory FM broadcast receiver if the band Width of the television sound channel and its associated FM discriminator is made sumciently wide. However. up to the present time, little use has been made of the television receiver components for the reception oi' standard broadcast AM signals falling within the range oi 540 to 1600 kc.

`It is therefore a purpose of the presentinvention to provide a simple and economical combination type television receiving circuit which not only provides reception and reproduction of televisioni signals but also at the expense of little additional circuitryprovides high quality reception of standard broadcast AM signals.

It is further a purpose of the present invention to provide a simple and economical adapting circuit i'or existing television receivers which will permit the receiver to be used in the reception of standard broadcast AM signals.

The present invention is further involved with the provision of a novel system of circuitry which permits the common elements of present-day 7 claims. (ci. rief-5.a) g

, Y. v 2; television receivers to be efciently utilized in the reception of standard broadcast AM signals.

In orderA to accomplishthe above objects, the present inventionr contemplates the use of a heterodyning circuit employing a fixed oscillator, having a frequency which, when added to the lowest frequency desired to be reproduced in a broadcast` band, will fall within the band pass characteristic of a 4standard television receiver video I. F.'amplier. .Rectifying means are then associated with the output of the television receiver video amplifier allowing the received AM standard broadcast signal to be demodulated and subsequently applied to the input of the sound amplier otherwise utilized for 'the amplification of FM sound derived from the television receiver sound channel.

Avfuller understanding of the operation of the present invention, as well as other objects and features of advantage in addition `to these set forth hereinabove may be readily gleaned from Ythe following specification especially when taken in connection with the accompanying drawing in which: .p Y

Figure 1` illustrates one embodiment of the present invention as applied to standard television receiver; and v p Figure 2 illustrates another-embodiment ofthe present -invention as applied to standard television receivers.

Referring now to Figure 1, there is represented by the block I0 some of the components of a typical modern-day television receiver including an R. F. amplifier and a converter. As is commonly the practice, signals intercepted by the antenna I2 are heterodyned by the television receiver converter to produce a sound I. F. signal for application to the sound I. F. amplifier represented by block I4 and a video I. F. signal for application to the video I. F. ampliier indicated by block I5. Accordingly, the output ofthe sound I. F. amplier isapplied to an FM discriminator indicated at block 18, whose output is generally coupled with thel input of an audio amplier 26 for reproduction of the sound ac-V companying the television transmission. The output of the video I. F. amplifier I6 is applied to .a video detector 22 to obtain' a video, signal which is thenapplied to the input of the `video amplifier 24. Theoutput of the video amplier 24 is conventionally applied to the input of Van image reproducing device, such as a kinescope. For ease in illustration, the kinescope itself has not been shown nor have the beam `Vdeiiection circuits .for thekinescope been indicated.

Purely by way of example, the sound I. F. ampliiier is illustrated as being designed around an intermediate frequency of 21.25 mc. While the video I. F. amplii'ieris illustrated as beine' designed for an intermediate frequency of 21.75 mc. It is to be understood that these numerical values arepurely exemplary and may in practice be found to assume variousothervalues as the particular design of the receiving equipnient dictates. Typical examples of the Weliknown circuit configurations in Aeach of the Acircuit blocks shown may be obtained in anzarticle entitled Television receivers by Antony Wright appearing in the RCA Review'lfor March 1947. Other examples of typical circuitlarrangements represented by the block diagrams may be found in an article entitled Video receiver 'circuits simplied by D. D. Cole in the magazine Tele- Tech for January 1949, as Well as in an article entitled Television receiving systems by C. M. Sinnett appearing J-in .the 'monthly publication Electrical l Engineering v`rfor Ju-ne 1949. "The receiving i frequency AVrange v.i'or mostcommercial television receiving circuits"is/madev to give reception `on channelsl` Ithroughl covering Ythe frequency range of '54. mc."to 216 mc.

Accordingtolthe embodiment of `'the `present inventionshown iin Figure l, there areI provided three discharge tubes-B, 139, Fand 132 'connected in .a well-'known -fo'rmbf balanced modulator type .of 'heterodyning circuit. T-he discharge tubes Ziandll are'` respecltivelylconlnected 'in va balanced ymodulator fashion- ?having an input' cirn cuit :deiined the' i-nductance-Sl 'S and capacitor 3E a-ndian output circuit Ydefined'bythe-inductance'SS. and Athe-capacitcrfili. The/os'cillatcr Y12 is,

by means of its resonant tank circu-itliL-rnade' to sustain vIoscillations at laf-requency 'fairly -close to :the 11F. frequency I off the" vidcoi.' F.- channel 16. inthe-'particular arrangement shown -infFig- .ure l, the oscillator is indicated .as being tuned to a frequency-Toi" 212125-mc-1' which is -thestandard intermediate frequency 'ffor the sound-arnplier i4 and which, as reference to theabove cited 4publications will show, isfthefrequency at which` the' video "1. F. amplifier i6 generally given a rejection characteristic. ZIhisrejection characteristic' vis employed to reduce Vther-possibility -of sound interference in theftelevisionfpicture. In general, however, the oscillatorZ -may be given any frequency which'whenladdedto the lowest broadcast frequency it is desired Lto' receive-'will 'yieldl a signal frequencyT falling Within the pass range of the video-'amplifier'- AI6.

Accordingly, .the A'heterodyn'e circuit is connected with the output of--any type of selective tuning system covering the .broadcast frequency range such as, vfor'example, indicated Yby the selectively 'tunable circuits 44 and-lian'd the'heterodyne input .circuit34. These 'selective -'elements 414,46 VAand 34 of the'tuning system are ganged Atogether in .such a VVVway as to- Vprovide tracking over -the Sentire `broadcast band. 'The input of the selective system may if lde'sired, be connected with-.any form of -antenna'fsuitable for picking up radio carrier frequenciesv in *the Alfibroadc'ast range. l As illustrated in Figure I1, the input'terminallllof thelt'uning'system 4iis coupled `with -theltrans'miss'ionline 50 of the-tele visionantenna. In thiswaygthe transmission line: vitself .acts as. an `AM broadcast :frequency antenna.

In' further accordance with' thepresent invention, heterodyne circuit-,output signal developed across -the inductaanceV 38 is coupled' by Ssome means such as the twisted pair 52 to the input of the video I. F. ampliiier at I6. In Figure 1, the coupling to the video ampliier is accomplished by the couplingtransformer 54. However, it will be understood that any convenient mode of coupling may be utilized.

`In the normal 'operationiof the television receiver 'ofFigure 1 the 'audio "ampliiier 20 is, by means of the switch shown at 56, connected with the output of the discriminator I8 While the oscillator 32 and the balanced heterodyne modu- Y latorcircuit and 30 may be disabled.

` However, when operating the circuit in accordance withthe present invention, the switch 56 connected'with the audio amplifier 20 is connected with'thc'output of the video amplier 24 and the'hcterodyne circuit comprising tubes 28. 3B and 32 is activated. Under such conditions AM broadcast signals will be heterodyned by the heterodyning circuit up to frequencies falling within' the video .1.113. band `o'fwtbc Aamplifier-SHS. 'Ihislwilizbe' evident .since the AM broadcast band is .'cmrly flabout Ione mc. wide. while the .video'l ampliiier for television receivcrfisgas 'pointed-lout hereinabove,:generallyin the'range fof 3 to #4 mc.'r wide.' .The thus .fheterodyned broadcast signails :willi then be :detected-by the videondetec'tor 22, whose output in" turn 'will-contain .audio'requency fcomponents corresponding -to the sound modulation i envelope 'ofi the AM. broadcast rad-io carriers. vThese audio "irequencysignais @will theniibeampliiiedby the video amplifier 124.and applied -tothe input of .the audio ampliierrtllfor sound. reproduction Vbythe' loudspeaker :among themany unique features -o'f'thepresent system, itu/ill.ibezappareritthat the l.use oi a fixedV frequency heterodyningioscillator eliminates the .'.annoysome- .tracking problem usually present .in conventional 9AM broadcast receivers. Furthermore,V becauseorilyasingle signalis-presentin theampliiierlatzany given .time very' little cross-modulation "will occur. v.'lVIoreover, the image interference will .beigreatly reduced because ci" fthe-.high intermediae :frequency tol which the Abroadcastband .carriers havey been-heterodynedtnrconve'rted.

en zalterna'tive embodiment of 'fthe .present vin ventionisiishownxin Figure L2. The general 'arrangement Yofrthie television receiving system is substantially thel saine. as lthatishown vin Fig-ure i and i corresponding .elementshave been assigned y like .numerical ldesignations.' Here againlthe -oscili'atcrA 32 :zis -tuned .to some frequency which, when added to .zthel'ow'est lbroadcast frequency Ydesired ...to "be reproduced, Lwill '.f-'all 'in thevideoi. passliban'd of theampliiieril. However, inlliigure'll .the balanced fmodulator circuit 'comprisingtubesidt and -ofliigure 1 has been replaced .byila single'. discharge tubel which has its input circuit coupled with both the output Vof the selective tuning. system andthe osciilatcn'r 32. Aiso,;in'ligure;2, the output ofthe heterodyne circuit tfis .shovmito v.be f-.capacitivei'y coupled tolthe rinput ci the video I; Fiampliiier l via capacitor.Y 62. .E It 'willi beiv further. seen'th'at since ia `single ended. type 'f of 1 heterodyne mixer has been employed, there-will bano' cancellation of the oscillator frecuicncyjgenerated.'byA the oscillator 'B2i Thus, there willbc1-a'rather high amplituder .oscillator `con-ipon'entV .present Iin the video I. F. amplifier itself.

With thearrangement of. Figure' 2, ithe operation of -the...1'3resentY .invention maybe regarded as .slightly different Vfrom vthat Aof Figure Y 1. Since theregis presentfn thevdeo I. F. amplifier I6 both the oscillator frequency and the intermediate frequency to which the AM broadcast carriers have been heterodyned, there will necessarily appear at the output of the video detector 22 the original broadcast carrier frequency being received which will fall within the range of S40-1600 kc. The video amplifier 2li, generally having a vfrequency response from 40 cycles to 4 mc., will then amplify this modulated carrier appearing at the output of the video detector. The output of the video amplifier may then be conventionally detected by means of a rectifying circuit such as 64. The audio voltage corresponding to the envelope of the received broadcast signals will then appear across the load resistance 66 which, in turn, may be capacitively coupled by capacitor 68 and on through the switch 56 to the input of the audio ampliiier 25. The rectii'ier E4 may be a separate rectifier or detector circuit set aside for this purpose alone or, as indicated in Figure 2, it may be nothing more than the television D. C. re-inserter diode for the video amplifier or kinescope. It is further apparent that in television sets employing a diode type of sync separator circuit that the sync separator itself could be employed as a demodulator circuit in accordance with the present invention.

The R. F. selective tuner comprising circuits 44, 46 and 34 may be made to assume a variety of forms without extending beyond the scope of the present invention. This R. F. tuner circuit may be designed to embrace more tuned circuits than just the three shown so that somewhat greater selectivity is obtained. Moreover, the design of the selective tuning system may be made somewhat more complicated to yield a more constant band width than the simple arrangement shown.

Having thus described my invention, what I claim is:

1. In a combination superheterodyne television and AM broadcast receiver having at least a superheterodyne converter stage for producing video I. F. signal at frequency f1, means for I demodulating frequency modulated sound intelligence corresponding to the video signal information, a sound amplifier for said demodulated sound, a video I. F. amplier for said video I. F. signal said amplifier having an attenuating characteristic at some frequency f2, a video detector for said video I. F. signal and a video amplifier for the output of said video detector, the electrical circuit arrangement comprising, a non-linear mixing circuit having at least two inputs and one output, a fixed oscillator developing a frequency substantially equal to f2, an adjustable tuning network for selecting and transmitting AM carrier frequencies within the broadcast band, means for coupling outputs of both said oscillator and said tuning network to the respective inputs of said mixing circuit, means for coupling the output of said mixing circuit to the input of said video I. F. ampliiier and means for selectively communicating the output of said video amplifier to the input of said sound amplier.

2. Apparatus according to claim l wherein said mixing circuit comprises a balanced modulator circuit wherein the output of said oscillator is applied as the modulator circuit carrier and the output of said converter is applied as the modulated circuit signal information.

3. Apparatus according to claim 1 wherein the magnitude of said oscillator signal applied to the input of said video I. F. amplifier is made suinciently large to produce a substantial video I. F. ampliiier output at the oscillator frequency and wherein said selective communicating means comprises a diode demodulator circuit having its input connected with the output of said video amplifier and its output connected with means for selectively applying said output to said sound amplifier input..

v 4. In a television receiving apparatus comprising a superheterodyne converter for producing amplitude modulated video intermediate frequency signals, a restricted bandpass amplii'ier for said video intermediate frequency signal, and a sound amplifier designated for normally communicating sound intelligence detected from frequency modulated signals accompanyingareceived video radio carrier, an amplitude modulation receiving arrangement for standard broadcast band frequencies comprising in combination a iixedvfrequency oscillator having a frequency which when increased by the lowest amplitude modulation broadcast carrier frequency will fall within the bandpass of said Video intermediate frequency amplifier, a tunable selecting circuit for broadcast frequencies, a heterodyning circuit having its input connected with the outputs of said oscillator and said selecting circuit, means for rectifying the output of said video intermediate frequency amplier and means for selectively applying said rectified output to saidl sound ampliiier for reception of amplitude modulated broadcast intelligence.

5. Apparatus according to claim 4 wherein said heterodynin'g circuit is of the balanced modulator variety so connected to minimize the amplitude of output signal at the oscillator frequency whereby the output of said rectifying means lis comprised mainly of signal variations representing the modulation envelope of the selected broadcast carrier.

6. Apparatus according to claim 4 wherein the oscillator frequency itself falls within the bandpass of said video intermediate frequency ampliiier and wherein said het'erodyning circuit is adapted to produce in its output a considerable magnitude of oscillator frequency whereby the output of said rectifying means is comprised mainly of signal variations corresponding to the carrier frequency of the selected broadcast carrier.

7. Apparatus according to claim 6 wherein said television receiving circuit includes a D. C. picture information restorer arrangement connected with the output of an amplifier designated and connected to communicate signals appearing at the output of said rectifying means and connections from the output of said D. C. restorer to the input of said sound amplier.

WINFIELD R. KOCH.

y REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,075,962 Roberts Apr. 6, 1937 2,270,652 Espley Jan. 20, 1942 2,491,808 Fyler Dec. 20, 1949 FOREIGN PATENTS Number Country Date 450,263 Great Britain July 14, 1936 

